In the early 1970's, the consumer products industry began substituting powder coatings for liquid and porcelain coatings on sheet metal based enclosures used in consumer products. For example, powder coatings are used on washer tops and lids, dryer interiors, microwave cavities, air conditioner wrappers, and office furniture. This was done to achieve better performance, increase coating application efficiency and to comply with new state VOC regulations.
Mass production of such consumer products has been previously accomplished by painting (both liquid and powder coating) the metal enclosures and the like, after the sheet metal used for the enclosure has been cut and formed into final, desired shape. This type of product finishing process is known as pre-forming.
Over approximately the last decade in the appliance industry, finishing methods have been changing. This change has been driven by the need to improve quality and reduce finishing costs. In particular, the appliance industry has successfully implemented a method commonly referred to as the "coil process." The coil process utilizes steel coils that have been pre-painted using liquid or powder coatings, prior to cutting and forming. The coil process has provided appliance manufacturers with substantial finishing cost reductions. The coil process requires that the manufacturer purchase the steel coil with the coating already applied by means of high speed, high cost, coil coating equipment.
While appliance manufacturer's have enjoyed the reduced cost benefits of this precoating/coil process, there are some major disadvantages that are associated with it. These disadvantages include the inability to control coating quality; bare, unpainted edges that reduce overall final product quality due to premature edge corrosion; and coated metal scrap which has a negative environmental impact. Other disadvantages stem from the complex nature of the high-production coil coating equipment, which requires a large capital investment on the order of 80-100 million dollars. Such large capital expenditures stifle supplier competition and inhibit further cost reduction. Furthermore, the high speed coating lines (350 feet per minute plus) associated with the coil process, require the use of solvent based coatings which negatively impact the environment and increase raw material costs.
These and other disadvantages have prevented the coil process from becoming the primary finishing method in the appliance industry and the like. In particular, only about 5-7% of all appliance enclosures are produced using the coil process.
The appliance industry has attempted to overcome these disadvantages, by utilizing pre-cut blanks of sheet metal which are then processed and powder coated using a high speed conveyorized transport system on the manufacturing site prior to forming into the final enclosure shape. This process is commonly referred to in the industry as the "blank powder coat finishing process."
In the blank powder coat finishing process, metal is blanked or precut into individual substrates which each have all their requisite pierces, notches and the like formed in them. This provides the advantage of having all the desired metal cutting performed prior to painting. Thus, all cut edges are powder coated thereby eliminating the presence of bare edges, which are a major source of corrosion. By comparison, the coil process cuts the metal after it is painted, which exposes bare edges, as well as generates scrap that is costly to the manufacturer and detrimental to the environment.
After blanking, each substrate is cleaned and pretreated with a chemical conversion coating; and then powder coated. The application of powder to the flat substrate (pre-coating) provides many advantages over post-coating of formed parts. For instance, the transfer efficiency can be high enough that reclaim overspray powder may not be necessary, especially with present state of the art application equipment. This reduces capital equipment costs and facilitates color changes. Further, pre-coating substantially flat blanks allows for greater film thickness control when compared to postcoating of formed parts since, the geometric complexity of the formed part makes its difficult to maintain the thickness of the paint film.
Once powder coated, the blanks are rapidly cured using infrared (IR) heating for part or all of the curing cycle. Rapid curing schedules enable the advantages of the blank process to be fully realized since, rapid curing allows substantial reductions in floor space. The IR heating allows very rapid upheat to the requisite powder curing temperatures. Accordingly, bake schedules of less than 60 seconds are possible which allows for typical IR oven lengths of as short as 50 feet. Additionally, since powder coatings are solvent free, they are well suited for short curing schedules where fast upheat rates are required, and produce exceptionally smooth films. With such rapid paint curing times, "blanking" line speeds are very high and can range from 50 to 80 feet per minute.
The fully cured painted blanks can be stacked for future use or immediately formed in existing forming equipment. In many cases, forming involves very sharp bends and/or metal drawing. Compared with liquid coatings, powder coatings have an exceptional balance of hardness and flexibility.
One can see that the blank powder coat finishing process substantially addresses all of the disadvantages of the coil process while providing similar or better cost reduction on a per part basis compared to the coil process. This is because blank powder coating systems require a capital investment on the order of only 3-10 million dollars, which is directly proportional to production tonnage requirements.
As mentioned earlier, the blanking line speeds in a typical blank powder coat finishing process can approach between 50 and 80 feet per minute. Such high line speeds require careful control and accurate setup for the chemical pretreatment, powder coating application, and curing. A mechanical problem or out of specification process will effect a large number of blanks in a short period of time because of the high line speed. Rapid access to all machine control functions for operation and maintenance is essential in order to properly operate as such high line speeds. Operators must continuously monitor the system for proper operation. System diagnostics and maintenance require the dispatching of skilled personnel to the location.
Accordingly, a need exists for rapid simple access to machine control functions by operators and maintenance personnel for the high speed conveyorized transport systems used in blank powder coat finishing processes.